The two teens accused of starting the fire that destroyed a historic Lynden building were held on suspicion of arson at their initial court appearance Wednesday afternoon.

The teens, ages 13 and 14, told police investigators that they had started the fire while in the third floor of the Delft Square building, according to a probable-cause statement read by Whatcom County juvenile prosecutor David Freeman.

The building was home to the Lynden Department Store before its closing in 1979. Before Monday afternoon’s massive fire, it housed several businesses, including a Japanese restaurant, a Whatcom Educational Credit Union branch, an art gallery, and a clock and antique shop.

The teens were allegedly in the building to smoke marijuana and “mess around,” they told investigators. The boys first began burning paper in a frying pan, which escalated to burning a box full of papers and a shirt, according to the charging documents.

Witnesses outside reported seeing one of the teens in a third-floor window of the building attempting to use a fire extinguisher on the growing blaze. Lynden Middle School administrators contacted police after rumors began spreading that one of the students there had started the fire.

One of the teens lives with his grandparents. Though the teens were originally arrested on suspicion of reckless burning, that charge was upgraded to first-degree arson, indicating that prosecutors believe the boys intended to set the fire. Both were charged with burglary as well.

Freeman declined to answer questions about the change in charges after the hearing and County Prosecutor Dave McEachran was not available for comment this afternoon.

Bail was set at $1,500 for both teens, who are required to submit to urinary analysis and a 7 p.m. curfew. Freeman also pushed for a mental-health evaluation for the boys, but Superior Court Commissioner Thomas Verge denied that request, saying there was no evidence that the boys suffered from mental-health issues. The teens will be arraigned on June 18.

Jeffrey Lustick, whose law firm is representing one of the teens, said he was “somewhat surprised” that the charges were upgraded to arson. He said the teen regrets his involvement in the fire.